Aircraft rotor and control thereof



oct. V11, 1949.

Filed Oct. 5, 1946 A. E. KOEPPE AIRCRAFT ROTOR AND CONTROL THEREOF 5 Sheets--Sheefl l INVEAITQILV ATTORNy5 Oct. l1, 1949. A. E. KOEPPE AIRCRAFT ROTOR AND CONTROL THEREOF 5 sheets-snee@ 2 lFiled 001;. 5, 194.6

Oct. 1l, 1949. 4A. E. KoEPPE 2,484,099

' AIRCRAFT ROTOR AND CONTROL THEREQF Filed oct. 5, 194e; s sheets-sheet s INVENTOR. n /V/n E. /foe e A T TOR/Vf Y5 Patented Oct. 11, 1949 UNITED STATES PATENT OFFICE AIRCRAFT ROTOR AND CONTROL THEREOF Alvern E. Koeppe, Grand Forks, N. Dak. l

Application October 5, 1946, Serial No. 701,434 2 claims. (c1. 17o-160.24)

This invention relates to airscrews, such as rotary wing aircraft rotors or propellers; and more particularly to an improved rotor structure and control means therefor, for use for example in helicopters and the like.

One of the objects of the present invention is to provide particularly for use in rotary wing aircraft a rotor mechanism of improved form whereby to obtain overall smoother operation. Another object of the invention is -to provide an improved airscrew for aircraft whereby to obtain improved efciency `and maximum thrust developments in return for a given power input. Another object of the invention is to provide an improved airscrew particularly for use in rotary wing aircraft whereby lift effects are uniformly distributed throughout the blade length; as a result of which an improved overall disc loading is obtained in combination with elimination of operational roughness characteristics such as are usually inherent in large rotors. Another object of the invention is to provide in rotary wing aircraft an improved rotor device so constructed and arranged as to avoid progressive stalling from tip Ito hub, and the usually attendant vibration eifects. Another object f the invention is to provide in rotary wing aircraft an improved rotor device which avoids unequal loading of the blade at different stations spanwise of the blade. Another object of the invention is to provide an improved rotor whereby to minimize profile and dynamic drag effects throughout the blade span under all operating conditions. Other objects and advantages of the invention will be apparent from the following specification.

It is believed that some attempts have been previously made to variably adjust different spanwise sections of the rotor blade to different angles of attack in accord with changing conditions of operation so as to equalize the loadings at different stations spanwise of the blade. Such prior attempts have been made by use of angularly adjustable flaps carried at the rotor blade trailing edges; but such attempts have not been fully effective and do not fulfill the purpose of the present invention because such prior art arrangements embody discontinuously profiled airfo'il sections whereby angularly changing airstream paths about the blade section are established, optimum aerodynamic efciencies are precluded, and vibration and lowered efficiency is inevitable.

The invention contemplates provision in a rotor of means for twisting the blade or blades thereof so as to progressively alter the angles of attack of the blades at different stations therealong, and to regulate the degrees of twist at the different stations so as to procure under all operating conditions equal aerodynamic loadings against all portions of blades in combination with maximum aerodynamic efficiencies at all stations spanwise of the blades. The invention may be practiced in connection with rotor arrangements wherein the blade roots are either fixed into a central hub, or in connection with a rotor arrangement wherein the blades are arranged to be individually articulated relative to a central hub. In the interests of simplicity of the drawing, however, the invention is illustrated and described herein in connection with a rotor comprising a hub pivoted to the helicopter mast and having a pair of blades xedto the hub and extending diametrically therefrom.

In the drawing:

Fig. 1 is a diagram illustrating graphically the different lineal velocities at different spanwise stations of the blade and the corresponding angles of adjustment of the angle of attack at such stations as are required to provide equal loadings on the blade at all spanwise stations thereof;

Fig. 2 is a fragmentary top plan, with portions shown in section, of a rotor hub and blade mechanism of the invention;

Fig. 3 is asection, on Yan enlarged scale, as along line III-III of Fig. 2;

Fig. 4 is a section, on an enlarged scale, along line IV-IV of Fig. 2; and

Fig, 5 is an enlarged fragmentary plan View of a portion of the rotor blade frame structure.

Fig. 1 graphically illustrates the relationship of angular velocity vs. lineal velocity or pitch of different portions of a rotor blade; the three portions of the blade selected for the purposes of the example herein being at the tip end and at the root end and at 'a midway position therebetween. The rotor hub is designated I 0, and the blade I 2; and the distance travelled by the tip end portion of the blade during one revolution of ythe rotor is graphically illustrated by the line OP. The distance simultaneously travelled by the midway portion of the blade is illustrated by OP; and the distance travelled by the root end portion of the blade is illustrated by the line O2P2. The linesOP, OP', and OZP2 are plotted tween these plotted lines vary as graphically illustrated by qb, B and a; and the graphical illustration of these angles in Fig. 1 indicates the different degrees of twist that should be imposed in the rotor blade at the correspondingstations in order to give the blade throughout its spanwise extent uniform aerodynamicloadings and to provide smooth and vibration-free rotor operations. Y Y Y Y Figs. 2.-5illust'ratemore specifically one physical form in which the invention may be exmany other types of rotor constructionsfvand that the example illustrated herein is not to he. construed to be limiting in any respect. The construction illustrated in Figs. 25-5: includes a tubu-# pressed, and it is to be understood that the in l vention Vmay be applied with .equal iatilwo lar drive shaft l5 which may comprise the rotorv Y mast in a rotary wing type aircraft, anda rotor hub 11S, which is connected to. one endof the shaftll by means oflalignedtrunni'on bearings lll-fliso, that the rotor hub is freev to pivot relativeltofthe mast. about. an axis transverse to the longitudinal. axisofj the mast. j

In. Fig. .2 .the rotor is illustrated to include a pariof bladesnvlfiichare indicated generally at HBP-2.0.. andin'clnde sparmembers 2.2,anchored inthe hub. .lt-IAS. explained' hereinabove, the present. drawing .illustratesapplication of the invention to,'a rotor construction wherein. the blade sparsi-extend incantilevergfashion. from the blade hubpand to.fthis;end.the spars 22 are illustrated tobra-keyed. as. at 2.4 into. the hub. Also, Vto re- .sist centrifugal loads the spars. are illustrated to .includeendthrustcollars 2li- 26. As illustrated infFig. 3 thefhuh ItV may be oftwo-.part form; the two halves being formedt'o. clamp upon4 the spar root ends and to be locked together thereon. by means. of.-Ybolts or-the like (not. shown) whereby the unit may. Ybe. iinallyfassembled into firmly loekedcondition..

The spars 2.2 will. beY preferably torsionally rigid throughout their lengths,.land. the. rotor blades tobe carried thereby. are illustratedv inY Figs. 4-5 .to-include pluraltiesofribs. 2'8. whichfare .ar- Yrangedin parallelspaced relation spanwise of the spars and rotatably mountedthereon as by means Yoi bearing devices asindicated at 3.0... Thus, the ribs 28 are selectively.rrv rotatable upon their ,mounting spare. unless otherwise restrained, and in order to control theangular. adjustments of theribs 2&1' contemplate. any suitable displacement typey control. means. connected to each of the -ribsvfor selectively adjusting the latter with respect-totheir angular positions aboutthe. axis of` the Vmounting spar.. For: example. as illustrated inthe drawingsv herein the rib control Vmeans may comprise Ya. plurality of. brackets 32 which .arey rigidly clamped. upon the spar 2.2. so 'astoextend. radially therefrom. in.rgid cantilever -fashionY adjacent the positions-.of thel ribs 255; Yeach-of Ythe brackets 32terminatingin a bearing portion 3d `(Fig-.#5) tofrotatably, accommodate a Ycamsshaft 35. f f Y e Y The-camshaft 35isf spanwisecoextensve with the Yrotor blade Zland` mountsnfkeyed relation thereon a-plurality-ofcamsisuch as-'are illustrated a-t'E-SSY (Figs.'Y4-5)'Y; one of said camsrbeing Adisposed-Y in` eachl instancewithina slot shapedy opening inl oneV of the ribmembers 2.3, as indicated at' SB'nFig. 5; Thelongaxes ofthe slotted openings Vare disposed'horizontally as viewed Vin 'Fig 41. whereby itvvill be understood that rotation'. of the cani shaft'` 35'; will! cause thetrailing ends of the ribs 28 to individually oscillate ver- Ystantially torsionallyr rig-id lengthwise of saidr blade and ,in generally' parallel rela-tion; av plurality. of. blade. ribsv jour-nalled. upon 4 tically upon the spar 22. Furthermore, the invention contemplates that the cams carried by the cam shaft will be of progressively greater eccentricities and /or sizes, ranging from the tip ends of the blades toward the hub. The cams will be preselected so as to procure the desired degree of twist at corresponding stations along the rotor blade; and thus it will be understood that -controlledfrotation of the cam-.shafts 35- Will accordingly'twist or warp; thebladezin s uch manner as to provide for maximum efficiency under all Yconditions of blade adjustment.

The ribs 28 are proled as illustrated in Figs. 3 4 in accordwvith` any desired airfoil section selection, anda. covering of any suitable material to .span the spaces between the ribs and to carry 'outtheprole contour thereof will be employed to envelop the spar-rib structure, as illustrated at @twig 2). As illustrated in Fig. 5, the ribs 28 may. be formedrto include top and bottom flange portions of laterally flaring contour asv indicated at d2 forbra-cing the ribYwebsecti'ons and the cov- Vering'material' against lateral bending under operative loads. Y

w To control the settingot the* cam shaft 35, the 4invention contemplates` any suitable'4 pilot-operable controlf mechanism such as may include, merely for purposes of example herein, a pinion 44" keyed to each cam shaft and arranged to be driven by a gear rack 45.' (Fig. 3') which is shown tobe vertically slidable relative-to thehub structure It and' guided thereby. toV remain in mesh with the. pinion 44.. Attheirlovver` ends the bars 45 may be arranged as indicated at 46 fo-rconnection to any suitable pilot-operable control mechanism, as througna wobble plate device or: the like; whereby it will be understood; that the rack bars 45' may be selectively displaced bythe pilot relative to the hub structure either simultaneously and equally for feathering. adjustments of .the rotor blades, or selectively and' unequally for cyclically unequalV adjustments thereof such as are useful in maneuvering control'r of theaircraft.

`As.illustrated in Fig. 2,tlxe cam shafts 35--35 are. .shown to be carriedupon frictionless bearings 48', and may include thrust collars 49 if desired. It is to be understood. that' althoughthe drawing illustrates the cam. shafts. 35 to be. disposed parallel'Yto. the spar tubes 22, the cam shafts may in lieu. thereof be arranged non-parallel to the spars .22- so. thatequal sized cams would bev adapted' to function to. provide the same type of twist adjustments referred to hereinabove.. Also, it will be understood that in lieu.A of the rotaryY cam and bearing. arrangements, illustrated at. 352.-39Vthe shafts 35 may be. formed` with radially extending horns of varying lengths which in turn. are connected' throughrsuitable link devices to. the corresponding rib. members ,forvariably rotating, the ribs-relative to the sparsfor thetwist adjustment pur-.poses set forth hereinabove.. Y

It` will Valsobe understoodl that although. only one form of the invention. has been shown and describedin detail, itvwill be. apparentty those skilled` in the art that theY invention is notl s0 'limited' but that various changes may be; made therein without departing` from the spirit ofthe invention or the scope ofthe/appended claims.v

VI claim: Y

lY. An airscrew'blade comprising, a pairsof subn spars.- extending a iirst one of said spars at intervals therealong and separately rotatable thereon, covering means carried by said ribs to provide the aerodynamic contour of said blade, and cam means carried by the second one of said spars at positions thereon in registry with said ribs and operable upon rotation of said second spar to separately rotate said ribs about said first spar to different degrees for twisting the aerodynamic shape of said blade.

2. A rotary wing aircraft blade comprising a hub, a substantially torsionally rigid spar extending from said hub lengthwise of said blade, a torque shaft journalled upon said hub and extending generally parallel to said spar, a plurality of blade ribs journalled upon said spar at intervals therealong and separately rotatable thereon, covering means carried by said ribs to provide the aerodynamic contour of said blade, and cam means carried by said torque shaft at positions thereon in registry with said ribs and operable upon rotation of said shaft to rotate said ribs 6 about said spar to different degrees for twisting the aerodynamic shape of' said blade, and means operable to rotate said shaft.

ALVERN E. KOEPPE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

